1. Field of the Invention
The present invention relates, in the field of the composite materials, to a multi-branch fitting, comprising at least three branches aimed at assembling parts forming an angle between them, as well as to a method for manufacturing such a multi-branch fitting.
Under multi-branch fitting, it is understood that a fitting comprises at least three flat or substantially flat branches or flanges extending radially from a joining area. The branches or flanges of these multi-branch fittings may not necessarily all be intersecting according to one and the same axis, and extend according to planes intersecting externally to the fitting. The most often used multi-branch fittings are particular cases such as T-, Y- or X-shaped fittings.
A multi-branch fitting made of composite material is essentially, but not restrictively, aimed at being used in the field of aeronautics, for example to connect two or more parts, and as a replacement for similar fittings hitherto made of metal. These fittings are aimed at being made integral with the parts to be connected and therefore provided, externally to the folding, with coupling areas aimed at permitting the assembling of said parts to be connected, in association with means for making integral, which may consist, non-restrictively, of gluing, riveting or screwing means.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
By way of an example, a multi-branch fitting of the state of the technique, in this case a T-shaped fitting, is shown in FIG. 1. This T-shaped fitting 1 includes a sole 10, in the form of a plate, and a transverse wall 11, which extends on one side 12 of said sole 10 while forming with the latter an angle, in this case a right angle, and which divides said sole into two parts 13 and 14, in this case having the same dimensions, the side of said sole opposite the one from which extends said transverse wall constituting a bearing face 15 aimed at entering into contact with one of the parts to be fixed, while either one of the two faces 16 and 17 of said transverse wall 11 constitutes a bearing face for one or several other parts to be fixed. This T-shaped fitting 1 includes a multiplicity of holes 18 aimed at permitting to fix the parts to be assembled, through joining means such as screws or rivets. Such a T-shaped fitting 1 is achieved by molding a composite material, more specifically from a fiber-reinforced thermoplastic or thermosetting matrix.
The replacement of the metallic elements by elements made of composite material is essentially imposed by the necessity of a weight gain. This has however drawbacks from the point of view of the strength.
It is indeed known that the weak point of the composite materials is the matrix, which has a much lower specific strength than the fibers. The range is for example of 20 MPa for resin and of 4000 Mpa for carbon fiber. Therefore, the collapsing of a part made of composite material is generally due to a breaking of the resin connecting the fibers, and in the case of a T-shaped fitting made of composite material the breaking is observed during a work essentially of unfolding and folding the transverse wall relative to the sole.
In order to cope with this drawback, it would be appropriate that the reinforcing fibers are subjected to the tensile and/or compression forces, and that the resin is not or little stressed. It is however not possible with the presently known techniques to achieve an optimal orientation of the fibers in such a part, except at a very high cost.
From W02010072952 is known an L-shaped fitting, made by molding a composite material, which comprises two portions forming an angle between them and drilled with holes in order to permit to make both portions integral by fastening means, at least one of said two portions having, on the inner side of said fitting, a concave curved profile, and more particularly a spherical or cylindrical profile, the hole or holes provided in same having an axis radial to the curvature.
This configuration permits the reinforcing fibers, or part of them, to be oriented in the direction of traction and/or compression, so that they are stressed by priority with respect to the resin.
However, such an L-shaped fitting cannot substitute a multi-branch fitting for assembling parts forming an angle between them; it does not have the required rigidity both for folding and unfolding. In order to replace for example a T-shaped fitting, two of these L-shaped fittings should then be used, as preconized in said WO2010072952, with the drawback of an uneasy implementation and an obvious failure of unicity of the part, resulting into an additional weight.